A hybrid vehicle using a high voltage battery includes a system automatically cutting off a power of a main high voltage battery at the time of generation of an emergency. The emergency means excessive electric leakage, insulation breakdown, or the like, due to aging of related components and excessive electric leakage, insulation breakdown, or the like, caused by a short circuit due to the destroy of components by external impact.
When the emergency is generated in a vehicle, an upper component controlling a high voltage component, such as a battery management system (BMS), a hybrid control unit (HCU), or the like, issues a command to cut off a main power to thereby cut off the power. The high voltage related component monitors a voltage and a current of a line connecting a power supply thereto through a series of programs or sensors and cuts off the main power through controller area network (CAN) communication or signal transmission when a voltage and a current that are out of a normal range are detected or there is a leakage current more than a tolerance and when there is insulation resistance breakdown more than a tolerance, or the like.
As such, it is very important to measure the insulation resistance in the hybrid vehicle using the high voltage battery. As a method for measuring a leakage current between a high voltage battery and a hybrid vehicle, there is a method of breaking down insulation and allowing a DC current to forcedly flow. This method has a disadvantage in that the insulation is broken down during measurement of an insulation resistance.
As a method for solving this problem, there is a method of connecting a coupling capacitor between a high voltage battery and a hybrid vehicle and applying an AC signal to the coupling capacitor to thereby measure an insulation resistance component. However, this method also has a disadvantage in that since a current for charging the coupling capacitor and a current discharged from the coupling capacitor should pass through the same circuit, there are many limitations in designing the circuit.
Therefore, in measuring an insulation resistance between a chassis ground of a hybrid vehicle and a high voltage battery, the demand for developing a small-sized, light, and a low cost insulation resistance measuring circuit capable of more simply and precisely measuring the insulation resistance has increased.